Sister sizes, simply explained
Sister sizes have approximately the same cup volume on different bands. Go down one band step and up one cup step for a tighter band; go up one band step and down one cup step for a looser band. For example, 32DD, 34D, and 36C are sister sizes.
They are alternatives, not interchangeable fits. Start with your measured size and only move one step at a time.
What are 34C sister sizes?
The sister sizes of 34C are 32D on a tighter band and 36B on a looser band. All three hold approximately the same cup volume, so if a 34 band feels slightly loose, try 32D; if it feels firm, try 36B.
Popular bra sister size groups
| Your size | Tighter band | Looser band |
|---|---|---|
| 32B | 30C | 34A |
| 32C | 30D | 34B |
| 32D | 30DD | 34C |
| 34B | 32C | 36A |
| 34C | 32D | 36B |
| 34D | 32DD | 36C |
| 36C | 34D | 38B |
| 36D | 34DD | 38C |
Frequently asked questions
What are 34C sister sizes?
The sister sizes of 34C are 32D (tighter band) and 36B (looser band). All three share approximately the same cup volume, so they are the first alternatives to try when a 34 band feels slightly loose or slightly firm.
When should I try a sister size?
Try a sister size when your cups fit well but the band does not: if the band rides up your back, go down a band and up a cup; if the band digs in, go up a band and down a cup.
Do sister sizes fit exactly the same?
They hold approximately the same cup volume, but the fit is not identical. Band tension, strap placement, and wire width all shift. Move one step at a time and check support and comfort.